RFR: Added section for newcomers [v6]

[Stuart Marks]

On Thu, 19 Nov 2020 04:58:18 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

>> Added a section to the introduction to set the expectations for new developers in the OpenJDK.
>> 
>> I also moved the mail list section up since it's also relevant in this context and should (imho) be the first thing to learn about when thinking about joining the community.
>
> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixed typos

Marked as reviewed by smarks (no project role).

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PR: https://git.openjdk.java.net/guide/pull/38